The parallel progression in energy demands over depleting oil reserves and rising greenhouse gas emissions entails a high risk of severe impacts on biodiversity, humankind food security and welfare. Thus, a new energy model is needed, based on greener and renewable energy sources, and cleaner as well as more sustainable fuel technology (Fortman et al., 2008; Jegannathan et al., 2009).

1.1 Biogas, syngas, vegetable oils blends and Fischer Tropsch liquids

The first response of heavy industry to the current energy and environmental problems includes some old systems, such as syngas and Fischer Tropsch liquids. Current advances in technology and engineering could bring new opportunities to these classical chemistry and biochemistry solutions, associated with fuel shortage situations such as the Arab oil embargo of the 1970s, or the Second World War. Some of these will be detailed below.

Removing lignin with alkaline chemicals such as dilute sodium hydroxide, aqueous ammonia and lime, has long been known to improve cellulose digestibility (Li et al., 2004). Among these alkaline reagents, sodium hydroxide (NaOH) has been widely used for pretreatment because its alkalinity is much higher than others, but it is also expensive, and the recovery process is complex. The following studies on various feedstocks illustrate this: Untreated cattails contain 32.0% cellulose, 18.9% hemicellulose and 20.7% lignin. Zhang et al. (2010a) reported that 54.8% of cattail lignin and 43.7% of the hemicellulose were removed with a 4% NaOH solution. The glucose yield from 4% NaOH treated cattails was approximately 80% of the cellulose available.

Adding addtional chemicals along with NaOH could improve pretreatment performance. Applying a NaOH and H2O2 solution helps in additional lignin removal through oxidative action on lignin. Maximum overall sugar yield obtained from high lignin hybrid poplar was 80% with 5%NaOH / 5% H2O2 at 80°C (Gupta, 2008). Zhao et al. (2008) discovered that a NaOH-urea pretreatment, can slightly remove lignin, hemicelluloses, and cellulose in the lignocellulosic materials, disrupt the connections between hemicelluloses, cellulose, and lignin, and alter the structure of treated biomass to make cellulose more accessible to hydrolysis enzymes. The enzymatic hydrolysis efficiency of spruce also can be remarkably enhanced by a NaOH or NaOH/urea solution treatment. A glucose yield of up to 70% could be obtained at the cold temperature pretreatment of (-15°C) using 7% NaOH/12% urea solution, but only 20% and 24% glucose yields were obtained at temperatures of 238°C and 608°C, respectively.

Two theoretical approaches were used to study the enzyme kinetics of sodium hydroxide pretreated wheat straw, and describe the influence of enzyme concentrations of 6.25-75 g/L on the production of reducing sugars. The first approach used a modified Michaelis-Menten equation to determine the hydrolysis model and kinetic parameters (maximal velocity, Vemax, and half-saturation constant, Ke). The second, the Chrastil approach, was applied to study all the time values from the rate of product formation, taking into account that in a heterogeneous system, these reactions are diffusion limited and the time curves depend strongly on the heterogeneous rate-limiting structures of the enzyme system.

Nicolas Carels

Fundagao Oswaldo Cruz (FIOCRUZ), Instituto Oswaldo Cruz (IOC), Laboratorio de

Genomica Funcional e Bioinformatica, Rio de Janeiro

Brazil

1. Introduction

The rapid rise in the price of crude oil, the decrease in oil reserves, security concerns and greater recognition of the environmental impacts of fossil fuels have generated considerable interest in biofuels as an alternative energy source. The revolution in transportation that occurred at the beginning of the last century created dependence of Western economies on the combustion of hydrocarbon fuels. The invention of the electric light bulb by T. A. Edison led to the installation of the first energy distribution plant in 1883 (in Roselle, New Jersey) and subsequently the electric grid came to the world. Because of the high rate (typically >90%) and ease of alternative to constant voltage conversion or vice versa, as well as mechanical conversion of electricity, the electric grid became the nervous system of our civilization.

During the 20th century, humanity created a foundation in which electric applications are used in all segments of society. This revolution is now creating a system of pervasive computing and is preparing society for the era of nanotechnologies and robotics. However, the electric grid is dangerously dependent on the availability of carbon-based resources such as coal and natural gas (Song, 2006). Human civilization is now challenged with finding renewable and environmentally friendly energy sources for feeding both our electric grid and our economic growth. For the next two decades, fossil fuels will continue to be the most cost-effective energy resource. However, despite their higher costs, alternative energies have begun to be seriously investigated. It is the purpose of the present work to provide an overview of this issue.

Existing fossil fuels are believed to have originated over the course of millions (M) of years (yrs) from biochemical and geochemical transformations of organic substances that were present on the earth’s surface. The geological storage of carbon in the form of fossil fuels can be viewed as one alternative route to the reduction/oxidation cycle of carbon that is occurring at the earth’s surface. Numerous studies have shown that coal is formed from biochemical degradation and geochemical maturation of higher-plant materials that were originally generated via photosynthesis. Crude oil also shows fingerprint molecules such as phytane that testify to its plant origin (Johnston et al., 2007).

Crude oil contains various hydrocarbons that range from light gases (e. g., C1-C5) to heavy residues (Fialkov et al., 2008). These hydrocarbons are separated via distillation into three main products, namely naphtha, middle distillate and a residual fraction. Naphtha (boiling range 90-190°C) is mainly used for motor gasoline (C3-C12) and comprises approximately 20% of the total crude oil. The middle distillate can be separated into two categories

consisting of kerosene-range products (light-end) and diesel-range products (heavy-end). The light-end middle distillates (25-30% of total crude oil, boiling range 150-260°C) are used for the manufacture of solvents, kerosene (C8-C16), commercial and military jet fuels (C3- C10) and light diesel fuel (diesel fuel No. 1, C8-C22). The heavy-end middle distillates (25­30% of total crude oil, boiling range 190-400°C) are processed to produce diesel fuel No. 2 (C10-C25) and heating oils (15-20%) (Kaplan et al., 1997). Lubricating oil (>C18) accounts for approximately 5-7% of the total crude. In addition to the alkane fraction, there is also a fraction of polycyclic aromatic hydrocarbons (PAH) whose relative importance in the composition of distillates increases from kerosene to heating oil. Beside the gas with green house effects (GHG) and their consequences on climate changes, it is the PAH that cause the most important environmental concerns because of oil spills. Actually, PAHs are rather resistant to microbial degradation (bioremediation) under anaerobic conditions, with the consequence that their removal from impacted environments is very slow. PAHs are also a source of concern regarding human health because they may stick to DNA, resulting in deleterious mutations and ultimately cancer.

World oil consumption is approximately 79 M barrels (bl) per day (a barrel is 159 l). The transport sector represents 50% of oil consumption (or 20% of energy consumption) and has an annual average growth rate of >2% per year. Energy demand worldwide is expected to rise by approximately 50%-60% over the next 20 years, reaching 112 M bl/day (Song, 2006). Most of the "cheap oil" that was (relatively) easily removed from the ground (and sold for US$ 20-30/bl) is already gone, and fossil fuel prices have risen over the past decades. The price of crude oil increased from US$ 18/bl in 1990 to US$ >100/bl in 2008 (Tan et al., 2008). Fuel prices will probably continue to increase in the future because of the following factors: (i) fossil fuel resources are limited; (ii) there is a lack of balance between supply and demand; (iii) the demand for fossil fuel is rising rapidly; and (iv) geopolitical instability and international conflicts are increasing (Rout et al., 2008).

With fossil fuel prices at US$ 45/bl, renewable energy from a range of biofuels is becoming economically competitive. Biodiesel fuel usually costs over US$ 0.5/l (as compared with US$ 0.35/l for fossil diesel fuel — see in Zhang et al., 2003) such that the increase in the use of biodiesel has been particularly rapid over the two last decades. It has grown from essentially zero in 1995 to more than 20 billion (G) liters (l) in 2009 (in the US as well as in Brazil). Brazil and the United States (US) have the largest biofuel programs in the world, with the European Union (EU) ranking in the third position.

Biofuels can potentially mitigate greenhouse gases, can provide means of energy independence and may even provide new employment opportunities. Because they are compatible with existing technologies, they will also alleviate natural resistance to change and may act as a medium to allow a "smooth" transition to alternative technologies (Shinnar & Citro, 2006) and regulations. Many countries are now utilizing biofuel products resulting from agriculture and forestry. The most commonly cited advantages of biofuels are as follows: (i) they are available from common biomass sources; (ii) they are integrated into the combustion cycle of carbon dioxide (CO2); (iii) they are compatible with environmental constraints; and (iv) they contribute to environmental sustainability. For example, biodiesel fuel prepared from vegetable oils or animal fats is compatible with common diesel engines and is therefore a potential alternative to fossil-based diesel fuel. Sulfate emissions resulting from biodiesel combustion are close to zero and the net contribution of CO2 from biofuels when considering their entire life cycle (i. e., cultivation, oil production and conversion to biodiesel) can be low. The rate of pollutant emission over the life cycle of biofuels is comparable with that of fossil diesel fuel; however, because it is renewable, biofuel combustion does not result in CO2 accumulation in the atmosphere (Agarwal, 2007). Actually, plants use solar energy to turn atmospheric CO2 and water into organic carbon and hydrogen, thereby storing energy. The organic molecules are then broken down as the plant decays and the carbon is returned to the atmosphere as CO2. When growing a crop for fuel, part of the biomass produced by the plant is used directly to produce energy and the CO2 that was originally metabolized by the plant is returned to the atmosphere during the combustion process. This CO2 is therefore "renewable" because it is simply a portion of the total CO2 that is involved in the natural cycle. However, to produce a biofuel, a certain amount of energy is required. This sophisticated process of production needs a significant energy amount for growing, harvesting and processing the necessary biomass.

The concept of "well-to-wheel" (WTW) is used to characterize the energy consumption that is required to complete the entire process of production and transport of a fuel (Gnansounou et al., 2009). The WTW analysis is often divided into the following five stages: (i) feedstock production, (ii) feedstock transport, (iii) fuel production, (iv) fuel distribution and (v) vehicle use. These stages can be divided even further into "well-to-tank" (WTT) and "tank-to-wheel" (TTW) processes. Fig. 3 in Agarwal (2007) shows that the rates of pollution with the corresponding increase in energy consumption of crude oil, natural gas, biomass, wind power are 1.3, 1.8, 7.1 and 45 times lower, respectively, than that of coal. Nevertheless, biofuels (such as ethanol and biodiesel) fall on a line with a slope equal to crude oil. However, the intercept is lower, which demonstrates that the benefit of biofuels over fossil diesel fuel is due to the recycling of the former through photosynthesis. More advanced technologies (e. g., synthetic fuels based on biomass gasification or wind electricity) use virtually only renewable energy for the conversion processes and result in very low GHG emissions.

Despite of the explosion in discovery of new materials with a wide range of possibilities, most of the PSA units existing in the market still use the well-known zeolites (4A, 5A and 13X), activated carbons, carbon molecular sieves, silica gel and alumina. Since the adsorbent material is the most important choice for the design of the PSA unit, more efficient materials should be employed to satisfy more market constrains (energy consumption and size). One interesting example of the possibility of application of new materials is the Molecular Gate technology, where the utilization of narrow pore titanosilicates (ETS-4) lead to a successful technology for CH4 upgrading (Kuznicki, 1990; Dolan and Mitariten, 2003). The ETS-4 materials when partially exchanged with alkali-earth metals present a unique property of pore contraction when increasing the temperature of activation (Marathe et al., 2004; Cavenati et al., 2009). This property is very important since the pores can be adjusted with a very high precision to do separations as complex as CH4-N2. Within this kind of inorganic substrates, other interesting material that deserves attention are the aluminophosphates. Even when these materials do not present a very high CO2 capacity, they have quite linear isotherms (ideal for utilization in PSA applications) and also some of them present Type V isotherms for water adsorption, which means that they have certain tolerance (and regenerability) if traces of water are present (Liu et al., 2011).

In the last years, a new family of materials with extremely high surface area has been discovered (Li et al., 1999; Wang et al., 2002; Millward and Yaghi, 2005; Mueller et al., 2005; Kongshaug et al., 2007). The metal-organic frameworks (MOFs) can actually adsorb extremely large amounts of CO2 when compared with classical adsorbents. Furthermore, it is possible to adjust the structure in such a way that the steepness of the isotherm is mild and thus regeneration is simpler. An example of this high CO2 loading on MOFs is given in Figure 9 where the isotherms of CO2 and CH4 on Cu-BTC are shown at different temperatures (Cavenati et al., 2008). Comparing these isotherms with the ones presented by zeolite 13X (Figure 3), it can be observed that the steepness of the isotherm is quite mild leading to much higher "cyclic capacity" than zeolite 13X. Several MOFs were studied to separate CH4-CO2 mixtures (Schubert et al., 2007; Cavenati et al., 2008; Llewellyn et al., 2008; Dietzel et al., 2009; Boutin et al., 2010). Most of them present excellent properties for CO2

adsorption, eventually with mild-non-linearity of CO2 isotherms. Issues to commercialize these materials are related to the correct formulation and final shaping without significantly loosing their surface area.

Fig. 9. Adsorption equilibrium of CO2 (a) and CH4 (b) on Cu-BTC MOF at 303, 323 and 373 K (data from Cavenati et al., 2008).

The extremely high CO2 loading of MOFs indicate that the size of the PSA unit can be significantly reduced using this material instead of classical adsorbents. Furthermore, the CO2 adsorption kinetics in several MOFs is quite fast, thus most of its loading can actually be employed per cycle. One of the main issues with MOFs is that water cannot be present in the system and should be removed in a previous step (which should not be an important problem since water must be removed anyway).

As mentioned above, the chemical catalysis of the transesterification reaction requires high temperatures to achieve an acceptable reaction rate. In the case of the alkaline catalysis, the minimal temperature to produce conventional biodiesel is 60°C, while in the acid catalysis the temperature ranges from 50 to 80°C (Robles-Medina et al., 2009). Acid catalysis is slower than the alkaline one and generates a more corrosive fuel, so alkaline catalysts are preferred by the industry. It incurs a great energy cost in order to initiate and maintain the reaction (Kawahara & Ono, 1979; Aksoy et al., 1988; Cao et al., 2008). However, the utilization of sodium hydroxide as a catalyst has a serious limitation in the form of saponification of free fatty acids if water is present. This drives the increased consumption of the catalyst and downstream processing problems, such as the separation of glycerol and unreacted precursors. The solutions to manage this problem include using only virgin oils, often edible vegetable oils, instead of oils with high free fatty acids and water content, such as waste cooking oils or animal origin fats, as well as other residual fats. Higher temperatures, up to 120°C, and the addition of organic solvents, or additional steps for free fatty acids esterification with sulphuric acid before performing the alkali-catalyzed transesterification are quite common as well (Jeromin et al., 1987).

When lipases are used as catalysts, it is possible to get over the saponification problems owing to their ability to transesterificate alcohols with both triacylglycerols and free fatty acids. Besides, lipases work as well in the presence of water. In fact, they need a certain hydric activity to maintain their tridimensional structure, so the presence of water is not a problem with this kind of catalyst — although excessive hydric activity affects the transesterification reaction because the substrates are water insoluble (Jaeger & Eggert, 2002; Shah et al., 2004; Gilham & Lehner, 2005; Fjerbaek et al., 2009). Lipases can operate at low or relatively low temperatures in the range of 20 to 70°C, and at even lower temperatures if the enzyme has been obtained from psycrophilic microorganisms (Dabkowska & Szewczyk, 2009). Depending on the chosen lipase and preparation (free, immobilized or whole cell catalyst), lower temperatures (below 65°C) can be applied to avoid the thermal denaturation of the enzyme, thus saving in production costs (Fukuda et al., 2008). Within the thermostable lipases, we can cite Burkholderia cepacia lipase (Amano PS lipase, from Amano Pharmaceutical Co., Japan), that reaches its highest activity at 60°C (Dabkowska & Szewczyk, 2009), and the lipases obtained from Thermoanaerobacter thermohydrosulfuricus

SOL1 and Caldanaerobacter subterraneous subsp. tengcongensis, which show their activity maximum at 75°C and tolerate temperatures as high as 95°C (Royter et al., 2009).

On the other side of the spectrum, the lipase from Bacillus sphaericus MTCC 7526 presents its optimal temperature at 15°C, keeping stable until 30°C, and the Microbacterium phyllosphaerae lipase presents the optimal temperature at 20°C and deactivates when the temperature exceeds 35°C, with the pH value fixed at 8 for both psycrophilic enzymes (Joseph et al., 2006; Srinivas et al., 2009). Therefore, pH plays an important role in the enzymatic production of biodiesel because it influences both the reaction rate and the thermal stability or solvents’ susceptibility of the lipases. An adequate pH can facilitate the optimization of the operation temperature and improve the activity of the enzyme. Gutarra and collaborators reported a high stability of the Penicillium simplicissimum lipase in the pH range 4.0-6.0, that showed the maximal activity at 50°C and remained stable and active (although with a lower activity) even at 70°C (Gutarra et al., 2009).

Hydro-cracking is less popular than the hydrotreating in the petroleum industry. Hydro-cracking is a thermal process (>350 °C, >660°F) in which hydrogenation accompanies cracking. Relatively high pressure (100 to 2000 Psi) is employed, and the overall result is usually a change in the character or quality of the end products (Ancheyta and Speight, 2007). This process is performed by dual-function catalysts, in which silica-alumina (or zeolite) catalysts provide the cracking function, and platinum and tungsten oxide catalyze the reactions, or nickel provides the hydrogenation function. Alumina is by far the most widely used support

Hydro-cracking is an effective way to make a large amount of light product, but it requires more severe conditions such as higher temperature and hydrogen pressure to deal with acids, which is not economical and energy efficient.

2.1 Bioethanol

The technique of alcohol fermentation has been known for thousands of years. Ethanol distillation has been carried out for decades by industry because it has been part of the process of the regulation of sugar prices on the international market. Ethanol is regularly produced from the isomerose (high-fructose syrup) of grain crops such as maize or wheat and from sugar crops such as sugar beet or sugarcane. In Europe, sugar beet is preferred. This is especially true in countries such as the UK, France, Holland, Belgium and Germany, where it is highly productive, as 1 ha of this crop can produce 5.5 t of ethanol, (1 ha of wheat only produces 2.5 t of ethanol) (Demirbas & Balat, 2006). These numbers must be compared to the ethanol production from sugarcane, which reaches 7.5 t in Brazil (Bourne, 2007).

The USA produces ethanol from corn, whereas India uses sugarcane, China uses sweet potatoes and Canada uses wheat. Countries such as China, Austria, Sweden, New Zealand, and even Ghana are now building their biofuels infrastructure around wood-based feedstocks (Herrera, 2006).

The growing area used for sugarcane production in Brazil accounts for 8 Mha (Brazil is 850 Mha). Sugarcane produces an eight-fold return on the energy that is used to produce it. One ton of sugarcane used for ethanol production represents a net economy in CO2 emissions equivalent to 220.5 when compared with fossil fuel. Thus, if rain forest is not destroyed to grow the sugarcane, ethanol from Brazilian sugarcane reduces greenhouse gas emissions by the equivalent of 25.8 Mt CO2/yr (Marris, 2006; Walter et al., 2010). Fortunately, the Amazon, the Pantanal and the Alto Rio Paraguai regions have been prohibited for sugarcane cultivation by government decree since 2009 to preserve these ecosystems. In 2009, ethanol accounted for approximately 47% of transport fuel used in Brazil. The "Flex" car fleet can use 100% of either ethanol or gasoline (Orellana & Neto, 2006). In fact, ethanol gives 20% to 30% fewer kilometers per liter than does gasoline and people adapt the blend in proportion to the best consumption/price ratio (Marris, 2006).

The ethanol export capacity of Brazil is currently ~8 Gl. The export-destination countries are mainly the US, the EU, Japan and Central America. Conservative estimates suggest that the area used for sugarcane production in Brazil should increase from 8 to 11 Mha by 2015. By government decree, the maximum possible area to be used for sugarcane cultivation has been limited to 64 Mha (i. e., 18.5% of national territory). In the short-to-medium term, Brazil is the only country that is able to sustain the emerging international ethanol market. For long-term establishment in the market, other countries, such as Australia, Columbia, Guatemala, India, Mexico and Thailand, will need to increase their exports (Orellana & Neto, 2006).

Brazil began ethanol production in 1973. At that time, it was heavily dependent on foreign crude oil, with nearly 80% of its oil being imported. It launched the program PROALCOOL in 1975 (Goldemberg et al., 2004) and began to offer subsidies and low-interest loans to bioethanol producers to increase existing capacity. A policy of price dumping was maintained by the government to boost the use of gasohol. The ethanol content of common gasoline was originally 5% and is now 25% by law (Pousa et al., 2007).

Following the same model as in the environmental analysis, an economic assessment is done to evaluate the different cropping alternatives considered for the region. Thus, a comparative economic result can be achieved. Life cycle costing (LCC) methodology enables the compilation and evaluation of the inputs, outputs and the potential economic benefit of a product system throughout its life cycle (Lee et al., 2009). There are different LCC approaches, depending on their target, the costs involved and the context of the LCC itself. LCC is used in many fields, such as building techniques and rebuilding (Nassen et al., 2008; Ouyang et al., 2009) and also military equipment (Huppes et al., 2004). However as a product oriented method is hardly used for agricultural processes.

Costs include investments linearly distributed during the years of use, as this study pretends to give a mean economic benefit for an exploitation period of a year (a complete season). The benefit is shown as a representative parameter of the viability of each scenario. Fig. 6 shows a simple diagram of the rapeseed processing and co-products use. This figure also shows schematically the production of rapeseed with the different inputs and its processing. The same input scheme is applied to wheat and barley.

Following the LCA-based LCC methodology, this analysis takes into account all the process stages. The benefit calculation is developed by modelling each crop type as well as the rapeseed processing stage. Each crop type requires its particular fertilization and crop protection products. Rapeseed processing stage is only considered when transformation of seed is required (SVO scenario). The use of diesel or SVO in the tractor is also considered to take the consumption and the corresponding fuel emissions into account.

Each scenario is obtained by the combination of different crop partitions, each one with its own conditions, as already explained. The different partitions are Barley, Barley-2, Fallow, Rapeseed, Wheat and Wheat-1; where Barley-2 and Wheat-1 stand for barley 2 years after rapeseed and wheat 1 year after rapeseed. The benefits obtained in each scenario are shown in Fig. 7.

Contributions to the benefit are higher or lower according the proportion of each crop partition. Rapeseed — when not processed — gives a higher benefit per ha than the other crop types. It is clear from the results that small scale processing of the rapeseed to sell the oil is not as economically feasible as direct rapeseed sell.

Using diesel or SVO as fuel options have been analyzed, performing a diesel price and taxes sensitivity analysis. Results of these analyses show that the Spanish granted diesel for agriculture is preventing SVO to be introduced as a fuel for agricultural exploitations. Current policies do not support specifically self-supply fuels for agriculture, thus being unable to compete with already implemented diesel exploitations.

It is clear that in the current economic conditions, applying crop rotation RWBBB with diesel as fuel (diesel seed scenario) is currently the best option. Very close to this option is the SVO seed scenario, which uses the same rotation scheme but destines part of the seed harvested to produce fuel for the agricultural machinery. Thus, it reduces the amount of diesel used in the exploitation. Diesel and SVO scenarios benefit is 15% and 11% respectively higher than reference scenario (current scenario).

4. Conclusions

This chapter explains the production and use of rapeseed oil as self-produced agricultural biofuel and analyzes its use in the study area. It also evaluates from an environmental and economic point of view the presented model.

The first three sections show the small-scale production technology to obtain rapeseed oil and analyse the best rapeseed variety for a specific zone. Similar studies are necessary to analyse the most appropriate variety for each region under study. The fourth section is a summary of the necessary modifications in diesel engines to work with straight vegetable oil, as long as showing real consumption data from an adapted vehicle. It also shows the use of rapeseed cake as animal food. In section 6 an exploitation model is presented, introducing rapeseed to the traditional crop rotation of wheat and barley and incorporating the seed processing and oil use. Section 7 and 8 show the environmental and economic results of the proposed model compared to the traditional rotation and the sole use of diesel in the proposed rotation.

In the proposed exploitation model, all co-products obtained from the rapeseed plant processing (straw, rapeseed cake, oil and seed) have a clear target (field, animal feed, biofuel and seeds market) and a defined market price. Thus, no waste products are generated. Furthermore, the SVO obtaining process is more sustainable than biodiesel production thanks to its lower energy consumption and the avoidance of chemicals use like methanol. Results for SVO and diesel fuel use in the proposed rotation with rapeseed are compared to current rotation. Life cycle assessment show the environmental impact category results using 6 CML non-toxicological impact categories. The environmental evaluation shows the preference for SVO in most categories, however some others show adverse results. The implementation of this exploitation model should take the latter into account to minimize them. On the other hand, economic feasibility is not clear in the current economic context. However, it might be feasible in future scenarios where the access to fossil fuels was limited. Moreover, small-scale production and consumption of SVO can revitalize rural economies and help them being less dependent on diesel fuel. Furthermore, this model can also be useful in less developed countries, where diesel fuel might be scarce or difficult to obtain. Additionally, research in fields such as crop sustainability, crop emissions and new varieties of plants, diesel engines modifications and new type of lubricants among others is promoted. More research is especially needed in the sustainability assessment of the proposed model along the whole life cycle.

Thus, the use of SVO in diesel engines is a real possibility that can be taken into account when considering small-scale biofuel production.

Kurt A. Rosentrater

United States Department of Agriculture, Agricultural Research Service

U. S.A.

1. Introduction

Modern societies face many challenges, including growing populations, increased demands for food, clothing, housing, consumer goods, and the raw materials required to produce all of these. Additionally, there is a growing need for energy, which is most easily met by use of fossil fuels (e. g., coal, natural gas, petroleum). For example, in 2008, the overall U. S. demand for energy was 99.3 x 1015 Btu (1.05 x 1014 MJ); 84% of this was supplied by fossil sources. Transportation fuels accounted for 28% of all energy consumed during this time, and nearly 97% of this came from fossil sources. Domestic production of crude oil was 4.96 million barrels per day, whereas imports were 9.76 million barrels per day (nearly 2/3 of the total U. S. demand) (U. S. EIA, 2011). Many argue that this scenario is not sustainable in the long term, and other alternatives are needed.

Biofuels, which are renewable sources of energy, can help meet some of these increasing needs. They can technically be produced from a variety of materials which contain either carbohydrates or lipids, including cereal grains (such as corn, barley, and wheat), oilseeds (such as soybean, canola, and flax), legumes (such as alfalfa), perennial grasses (such as switchgrass, miscanthus, prairie cord grass, and others), agricultural residues (such as corn stover and wheat stems), algae, food processing wastes, and other biological materials. Indeed, the lignocellulosic ethanol industry is poised to consume large quantities of biomass in the future (Agrawal et al., 2007; Alexander and Hurt, 2007; Cassman, 2007; Cassman et al., 2006; Cassman and Liska, 2007; Dale, 2007; De La Torre Ugarte et al., 2000; Dewulf et al., 2005; Lynd and Wang, 2004). At this point in time, however, the most heavily used feedstock for biofuel production in the U. S. is corn grain. Industrial-scale alcohol production from corn starch is readily accomplished, and at a lower cost (generally between $1/gallon and $1.4/gallon), compared to other available biomass substrates in the U. S. The most commonly used process for the production of fuel ethanol from corn is the dry grind process, the primary coproduct of which is distillers dried grains with solubles (DDGS) (Figure 1), which will be discussed subsequently.

Corn-based ethanol has been used as a liquid transportation fuel for more than 150 years, although up until recent times the industry has been quite small. The modern corn-based fuel ethanol industry, however, has reached a scale which can augment the nation’s supply of transportation fuels. In 2008, for example, ethanol displaced more than 321 million barrels of oil (Urbanchuk, 2009), which accounted for nearly 5% of all oil imports. Only recently has this industry become truly visible to the average citizen. This has been due, in part, to the growing demand for transportation fuels, escalating prices at the fuel pump, positive

economic effects throughout rural America, as well as questions and controversies surrounding the production and use of corn ethanol.

To help meet the increasing demand for transportation fuels, the number of ethanol plants has been rapidly increasing in recent years, as has the quantity of fuel ethanol produced (Figure 2).

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In 2005, 87 manufacturing plants in the U. S. had an aggregate production capacity of 13.46 billion L/y (3.56 billion gal/y). At the beginning of 2011, however, that number had risen to 204 plants with a production capacity of nearly 51.1 billion L/y (13.5 billion gal/ y), which is an increase of nearly 380% in six years (RFA, 2011). Most new ethanol plants have been dry-grind facilities (Figure 3), which will be discussed subsequently. And, over the next several years, the

Renewable Fuel Standard (RFS) mandates the use of 15 billion gal/y (56.8 billion L/y) of renewable biofuels (i. e., which will primarily be corn-based ethanol) (RFA, 2009a), although the RFS does mandate the growing use of advanced and cellulosic biofuels as well. Because the industry is dynamic and still evolving, these current production numbers will surely be outdated by the time this book is published. As production volume increases, the processing residues (known collectively as "distillers grains" — will increase in tandem (as shown in Figure 2). It is anticipated that over 40 million metric tonnes (t) of distillers grains (both wet and dry) will eventually be produced by the U. S. fuel ethanol industry as production reaches equilibrium due to the RFS.

It is true that as the industry has grown, the concomitant consumption of corn has grown as well (Figure 4). Since 2008, for example, over 30% of the U. S. corn crop has been used to produce ethanol. When examining these numbers, however, it is important to be aware of several key points: exports have been relatively constant over time, there has been a slight decline in the corn used for animal feed, and the overall quantity of corn which is produced by U. S. farmers has been substantially increasing over time. Thus, it appears that the corn which is used to produce ethanol is actually arising mostly from the growing corn supply. It is also important to note that the corn which is redirected away from animal feed is actually being replaced by DDGS and other ethanol coproducts in these animal feeds. Thus coproducts (especially DDGDS) are key to the sustainability of both the ethanol and livestock industries. In other words, fuel, feed, and food needs can be simultaneously

1.2 The first problem: organic matter of digestate is poorly degradable in soil, its labile fractions were already utilised in a digester

The point is that the digestate is not an organic fertiliser because its organic substance is poorly degradable. But its liquid fraction contains a small amount of mineral nutrients, mainly of nitrogen. The fugate (and also the digestate) can be considered as a very dilute mineral fertiliser, nitrogenous fertiliser. However, the agriculture sector is exposed worldwide to an enormous pressure on economic effectiveness while the costs of machinery, fuels and agricultural labour force are very high in relation to the price of agricultural products. Therefore the chemical industry helps farmers to save on transportation and application costs incurred by fertilisation when highly concentrated mineral fertilisers are produced. Even though they are substantially more expensive, from the aspect of cost accounting their use will finally pay off. Before the manufacture of town gas from coal using the ammonia water ended, farmers took the waste containing 1% of ammonia nitrogen only exceptionally even though it was practically free of charge.

With the current output of a biogas plant 526 kW (Chotycany, South Bohemia) and daily dose of a substrate to the digester 46 t and practically identical production of digestate the daily production of mineral nitrogen is approximately 40 kg, which amounts to a relatively high value per year, almost 15 t of mineral nitrogen, but the dilution is unacceptable.